Island



UNITED STATES PATENT OFFICE.

ALBERT COTTRELL, OF NEWPORT, RHODE ISLAND.

METHOD OF BUILDING BRIDGES.

Specification of Letters Patent N o. 2,334, dated November 10, 1841.

To all whom t may concern.'

Be it known that I, ALBERT Oor'rRELL, of Newport, in the county ofNewport and State of Rhode Island, have invented a new, useful, andimproved method of building bridges whereby the same may be erected orprojected over a river or stream without the aid of centering and by avery simple, efficient, and substantial system of truckwork or framing,and that the following is a full and exact description of the same,reference being had to the accompanying drawings, which taken inconnection herewith form my specification.

In said specification, I have set forth the principles of my inventionby which it may be distinguished from others of a like character,together with such parts or combinations as I claim, and for which Isolicit an exclusive property to be secured to me for fourteen years byLetters Patent.

The nature of my invention, and the distinguishing feature of the same,consists in supporting the bridge during the process of construction, aswell as after completion, by the application of a counterbalancingpower, which, as will be hereafter explained, consists of stone laidupon a part of each end of the bridge, projecting in rear of itsabutment, thus preventing a depression or sag of the bridge, as is thecase with all wooden structures of this kind, and at thesame time givingto the bridge the appearance of a very flat segment or arch. On my plana bridge may be erected of any required span, without sustaining piersbetween the abut-- ments, and consequently as I shall herein afterexplain, I can commence the bridge on one side of the river, and by acontinual addition to the balancing power, I can project the bridgeacross the stream, without the use of centering, and when continued asuiiicient length, on removing a suitable quantity of the balancingmaterial, the opposite or projected end of the bridge, may be loweredupon the abut-ment on the other side of t-he river, and when this end isproperly weighted, the operation is completed.

In the drawings above mentioned, Figure 1, represents a side elevationof a bridge, constructed on my improved plan. Fig. 2, is a Verticallongitudinal and central section of the same. Fig. 3 is a top view, andFig. 4, is a vertical cross section of it.

In order to construct this bridge after preparing the abutments, itbecomes necesbridge.

sary to commence it at a point, siutated some distance back from t-hefront face of the abutment, or at a point A, Fig. 1, at a dis tance A B,from the point B. The bridge is then built from this point, (on a smallinclination above the horizontal line of the top of the abutments),toward the opposite side of the river. As the length of the structurebeyond the irst abutment is increased, it becomes necessary to place orpile stone C, Figs. 2, 3, on the top of that portion of the bridge inrear of the abutment-thus balancing and sustaining the bridge so built,until it reaches the opposite side of the river, and is of sufiicientlength to extend over the other abutment or from D to E as seen in Fig.l. The end of the bridge over the second abutment is then to be weightedwith stone, in a similar manner to that first described. The extremitiesof the bridge being thus depressed, lift the central part of it, therebygiving the structure the appearance of a very flat arch or curve. Thusit will be perceived that the gravitating power or weight of the bridge,between the abutments, is counteracted by thelstone laid on the top ofthose portions of the truck extending in rear of them.

Having thus explained the general principle, on which the bridge isthrown over a river, I shall now proceed to describe the system on whichthe same vis constructed.

The two side trusses are composed of planks, generally about one footwide and six inches in thickness. In the bridge represented by thedrawings it will be seen, thateach side truss consists of three stringpieces or beams F, G, H, each formed of planks a, a, Figs. 1, 2, 3, 4E,laid side by side and so arranged as to break joints over each other.They are connected together on their exterior and interior sides bydiagonal braces Z9, b, I), &c., c, c, 0, &c., crossing each other atright angles, as seen in Figs. l, 2, lying flat against the sides, andconfined to, the stringers at each of their extremities and centers inapposition, by a turned, cylindrical, wooden screw bolt (Z, (Figs. l, 2,3, 4, and more particularly denoted in Fig. 5), passing through thebraces and stringers from the exterior toward the interior of the Thediameter of this bolt is one third of the width of the brace and depthof the Stringer, a cylindrical hole of corresponding size, to receivethe bolt, being bored through the two braces and string piece at theircommon intersection or crossing of each other. The screw bolt shouldhave a strong head e turned on one end and a stout threaded screw cut onthe other, and may be formed of hickory, oak or other suitable hardwood. A. square or other proper shaped wooden nut f, is to be screwed onthe screw of the bolt CZ, so that when the bolt is passed through thebraces and stringers, they may be drawn closely and tirmly tow gether byscrewing up the nut.

The side trusses, so constructed, are connected together at top andbottom, by diagonal braces g, g, g, h, it, It, and counter braces z',z', 7c, 7c, 7c, as seen in the figure. These braces and counter bracesare conined to the top and bottom string pieces of each truss, and alsoto a central and longitudinal streamer or beam I or K, (formed of plankslike the stringers, but with the planks laid upon each otherhorizontally instead ot vertically, as in the string pieces, by screwbolts, passing through them and the stringers and each streamer, attheir lapping, exactly similar to those before described. The ends ofthe braces and counter braces are lapped upon the string pieces, midwaybetween the diagonal side braces and extend across, from one truss tothe opposite, in diagonal directions so as to cross each other at rightangles as seen in Fig. 8. It will thus be seen that regular system ofbracing and counter bracing, in vertical and horizontal directions isadopted. All the braces and counter braces should be formed by onepattern and of exactly the same dimensions, that is to say, thedistances between the centers of the holes in their extremities, and thecenter hole of each should be equal. The planks forming the stringersand streamers, should also be alike in their lengths and otherdimensions, and should have cylindrical holes bored through them at suchdistances apart as will permit the disposition of the braces and counterbraces, and connection of the same thereto by the wooden screw bolts.hen the timbers are t-hus previously prepared, the bridge may becommenced on the abutment, and carried back therefrom, a sutiicientdistance, to admit a quantity of stone or other heavy material to beplaced on the top of this part of the bridge, as was hereinbetoredescribed. The planks, forming the string pieces, are then applied tothose portions of the same, projecting over the river from the front ofthe abutment. rIhe succeeding` braces and counter-braces are thenarranged in position, and the screw bolts passed through them and thestringers thus securing` the who-le together. This operation is t-huscarried on, until the trusses are completed and reach over and extendbeyond the opposite abutment. Stone or balancing weight is thendeposited on the projected end, to such an extent as may be deemednecessary to compete with the weight of the trusses and prevent anysagging arising from the same or from the travel which may at any time,pass over the bridge.

In order to strengthen the side trusses ot the bridge, at the ulcra orbearing parts over the front wall of the abutments, several of thebraces on each side of the truss, may be continued of greater lengththan the others, thus making a triangular addition to each truss asrepresented at L, M, N, O, P, Q, Fig. l. The braces so lengthened, areto be bolted by wooden screw bolts, as was before described, to stringpieces R, S, constructed similar to the lower stringersi, but shorter asrepresented in the drawings. It is evident that any number of the bracesmay be thus arranged and bolted to the string pieces, so as to increasethe height of each trap above its points of support, to any extent thatmay be deemed desirable, to insure the proper degree of strength andstitiness to the bridge at the above mentioned points, It is only acontinuation of my system of bracing in equal squares. For bridges ofdifferent spans and widths, the number of trusses, stringers, braces andstreamers must vary according to circumstances. Where two carriagetracks are required, three trusses will in general be necessary, placedvertically and parallel with each other, and connected together at topand bottom, by braces and counter braces extending diagonally acrossfrom one outside truss to the other on the top and bottom sides of eachtop and bottom Stringer of each truss, those, on the upper sides of eachstringer crossing those on the lower, at right angles as beforedescribed, and the whole being secured to the trusses by wooden screwbolts.

The above constitutes the method of con structing the trusses. Thetimbers or planks, composing the following, may be applied to the topsof the lower stringers and streamers, in any convenient manner, butgenerally speaking, I prefer that the planks should be of the sainethickness, as the braces extending diagonally across on the tops of thelower stringers 0I'1 the trusses, and be laid upon the lower stringers,parallel with, and between the said braces, so as to form, in connectionwith them, the ooring. The horizontalbraces and counter braces of thelower stringers may be extended beyond the stringers on one or bothsides of the bridge, and connected by wooden screw bolts, with anexterior streamer at their intersections, over and under which they lap.This extension of the braces and counter braces, will admit of asidewalk being formed thereon on the exterior of the bridge. The upperhorizontal braces'and counter braces may be similarly extended over thesides, as represented in Figs. 3, t at the ends of the bridge in rear ofthe abutments, for the purpose of receiving thereon a portion of thebalancing material, thereby rendering it unnecessary to construct thoseparts in rear of the abutments so long as would be otherwise requisite.

The above geometrical arrangement and ldisposition of the timbers of thetrusses, and

horizontal top and bottom diagonal braces and counter braces, in equalsquares, secured by the wooden screw bolts and wooden nuts, admits theconstruction of a bridge of any desirable proportions, as will bereadily understood by bridge builders, and also produces a structure,where the top and bottom timbers, by being thus connected with the sidetrusses, greatly contribute to the strength of the same and render abridge, generally speaking, less liable to be ail'ected by violent windsand floods than when built according to other modes.

The substitution of one cylindrical wooden screw bolt, at the junctionof the braces and stringers, for treenails, as used in lattice bridgesis a great improvement for the great strain, brought on the treenails,from various causes, almost invariably, sooner or later, splits theplank and endangers the stability of the bridge, while the singlecylindrical bolt permits an equalization of the strain, and an easyaccommodation of the parts to each other as the work progresses, as wellduring the process of construction as, when completed.

Having thus described my invention I shall claim- Projecting a bridgeover a river, without the aid of centering, staying or supports, asrequired by ordinary bridges, by the application of stone or othersuitable counter balancing material, on the top of a portion of thesame, and in rear of the front wall of one abutment, thus supporting andsecuring the bridge on the abutment, as its parts are progressivelycombined together, and built over the stream toward the opposite sidethereof; also preventing the bridge from sagging in the center andgiving a flat curve to the same, by loading both sides thereof withstone, the whole process being substantially as hereinbefore described.

ln testimony that the foregoing is a true description of my saidinvention and improvements I have hereto set my signature this sixteenthday of August in the year eighteen hundred and forty one.

ALBERT COTTRELL.

Witnesses:

HENRY V. BOWEN, SETH HOWARD.

